House dust acari inhabit and propagate mainly in highly moist places, for example, on the surface of the floor, under or within the floor spreads such as tatami or carpet or within bedclothes. Recently, Dermatophagoides including Dermatophagoides pteronyssinus and Dermatophagoides farinae, which amount to 90% of these house dust acari, have become a serious problem since they are important allergens causing bronchial asthma, allergic rhinitis and atopic dermatitis.
The most effective method for exterminating these acari is to well ventilate and dry a house. However, the recent increase in houses of a closed structure and changes in life style make it more and more difficult to sufficiently ventilate a room. Under these circumstances, the damage by acari has become more and more serious.
In order to exterminate these acari, various acaricides (for example, organophosphorus compounds such as fenitrothion, fenthion, dichlorvos, diazinon; carbamate compounds such as propoxur, carbaryl; pyrethroid compounds such as resmethrin, phenothrin, permethrin) have been applied in the form of an aerosol, fumigant, insecticidal sheet or impregnating agent for, for example, carpet. Furthermore, it is recently proposed to use compounds other than those cited above for exterminating acari. For example, JP-A-61-57501 discloses to use a combination of acaricidal compounds such as benzyl benzoate, benzyl salicylate or dibutyl phthalate with a powdery cleanser and describes that the acaricidal effect of benzyl benzoate has been physiologically studied well in particular. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".) JP-A-61-91103 discloses an acaricide which comprises benzyl benzoate and an aliphatic hydrocarbon as the major components. Further, JP-A-61-87603 discloses benzyl salicylate and phenethyl benzoate while JP-A-62-33106 discloses phenyl salicylate, phenyl benzoate, diphenylamine, methyl .beta.-naphthyl ketone and coumarin each as an active ingredient for an acaricide. Furthermore, JP-A-64-19004 discloses an acaricide comprising benzaldehyde or perillaldehyde, l-carvone or d-carvone, methyl salicylate or ethyl salicylate, or methyl benzoate or ethyl benzoate as an active ingredient. Regarding natural substances, furthermore, JP-A-63-104905 discloses that terpene compounds are available as a preventing agent of acari. Furthermore, it is known that other vegetables essential oils (for example, bitter almond oil, wintergreen oil) show an acaricidal effect (F. Watanabe et al., Shoyakugaku Zasshi, 43 [2], 163-168 (1989)).
However, typical known acaricidal compounds (namely, organophosphorus compounds and carbamate compounds) generally show a high toxicity and exert undesirable effects on the human body. Therefore, it is undesirable to use these compounds indoors or around houses. These compounds are further disadvantageous in that their effects on Dermatophagoides causing allergic diseases are limited. On the other hand, pyrethroid compounds are expensive and show only limited effects on house dust acari, though they are less toxic in general. Other acaricidal compounds are also disadvantageous in the limited effects on Dermatophagoides.
Accordingly, it has been urgently required to develop an acaricide which is highly safe to the human body, can be easily used anywhere in a house and yet exerts an intense effect of exterminating a number of house dust acari including Dermatophagoides causing allergic diseases.